Automatic pipette



f April 14, 1970 Filed May 51, 1968 Zigi? [wm] l l l(I t?! a5@ 472;# 3739 1'/ 35? 26 f 3 35/ 52 25, kl 261%5/ 32 27 E J 19 Z'QL 30 2 3Q 20g 2521- J7 3 Sheets-Sheet 1 Oggi ""llllll Sqf/ -APril14, 1970 T. E.wElcHsELBAuM ET A1. 3,506,164

AUTOMATIC PIPETTE I s sheets-sheet 2 Filed May 31 1968 pe www?.

.4 7 TOPA/fy T. E. wElcHsELBAuM ET AL 3,506,164

April 14, 1970 AUTOMATIC PIPETTE Filed May 31; 1968 3 Sheets-Sheet 5raefvfy United States Patent O 3,506,164 AUTOMATIC PIPETTE Theodore E.Weichselbaum, Normandy, and Gene Sperry,

Bridgeton, Mo., assignors to Sherwood Medical Industries Inc.

Filed May 31, 1968, Ser. No. 733,337 Int. Cl. B67d 5/42 U.S. Cl. 222-340Claims ABSTRACT OF THE DISCLOSURE A pipette adapted to draw a variablepredetermined volume of liquid into a reservoir and thereaftercompletely dispense all traces of said liquid. The pipette comprises abarrel, a piston reciprocal in the barrel, a plunger operable on thepiston to cause axial displacement thereof, and automatically operatingindexing means responsive to the stroke of the plunger and piston in thebarrel providing a relatively shorter positive-stopped intake stroke anda relatively longer positive-stopped dispensing stroke so as to insurethat all traces of the liquid drawn into the reservoir on the intakestroke are completely dispensed on the dispensing stroke.

This invention relates to liquid transferring devices and, moreparticularly, to pipettes adapted to receive and dispense predeterminedvolumes of liquid.

Various scientific, industrial and medical analytical procedures requirequick and easy transfer of predetermined volumes of liquid from onereceptacle to another. A form of device commonly used for this purposeis a pipette having a barrel and a piston reciprocal in the Ibarrel,whereby upon a first intake stroke of the piston in the barrel, apredetermined volume of liquid is drawn into a reservoir, and upon asecond dispensing stroke of the piston in the barrel, the liquid isdispensed therefrom. One major problem associated with this type ofdevice is that of insuring that all of the liquid drawn in by the intakestroke is completely dispensed by the dispensing stroke. If the lengthof the dispensing stroke is the same as that of the intake stroke, traceamounts of the liquid will generally remain in the reservoir and fail tobe dispensed, which, depending upon the sensitivity of the analyticaltest being run, may seriously affect the reliability of the test.

Various attempts have been made to overcome this problem by providingdevices allowing an intake stroke somewhat shorter than the dispensingstroke. Heretofore, however, these attempts have not proven to becompletely satisfactory for accomplishing the intended purpose for thereason that the stopping point for the intake stroke on such devices hasnot been a positive stop but rather a semi-stop, requiring caution onthe part of the operator to avoid being overshot.

It is an object of this invention to provide a pipette of the barrel andreciprocating piston type which is adapted to drawn a predeterminedvolume of liquid into a reservoir and thereafter positively completelydispense all traces of said predetermined volume of liquid.

Another objects of this invention is to provide a pipette having thefeatures of the foregoing object which is adapted to provide adispensing stroke of the piston Within the barrel longer than the intakestroke so as to insure that all traces of the liquid drawn into thereser-vior on the intake stroke are completely dispensed on thedispensing stroke.

Another object of this invention is to provide a pipette having thefeatures of the foregoing objects and having a positive stopping pointfor the intake stroke short of the positive stopping point for thedispensing stroke.

3,506,164 Patented Apr. 14, 1970 A further object of this invention isto provide a pipette having the features of the foregoing objectswherein the positive stopping point for the intake stroke is adapted tobe brought into operational position only on alternating forward strokesof the piston in the barrel.

Still another object of this invention is to provide a pipette havingthe features of the foregoing objects wherein the operationalpositioning of the positive stopping point for the intake stroke onalternating forward strokes of the piston in the barrel is accomplishedautomatically by means responsive to the operating stroke of the pistonin the barrel.

Other objects and advantages of the present invention will becomeapparent from the following detailed description and accompanyingdrawings.

The above objects are accomplished in accordance with the presentinvention by providing a pipette comprising a barrel, a pistonreciprocal therein, an axially displaceable plunger operable on thepiston to cause forward movement of the piston inthe barrel, a returnspring for biasing the piston and plunger rearwardly in the barrel, andindexing means within the barrel for effecting engagement of a rst setof positive stopping means upon a first forward stroke of the plungerand piston within the barrel, and a second set of positive stoppingmeans upon the next Isucceeding forward stroke of the plunger and pistonwithin the barrel. The rst set of positive stopping means permits arelatively shorter stroke and is employed for the intake stroke whereasthe second set of positive stopping means permits a relatively longerstroke and is employed for the dispensing stroke. The indexing meanscomprises an axially displaceable and circumferentially rotatable memberdisposed within the barrel between the piston and plunger and isautomatically operative in response to the forward and return strokes ofthe plunger and piston within the barrel, as explained more fullyhereinafter.

In the drawings, in which like reference characters refer to similarparts throughout the several views:

FIGURE 1 is a front elevational view of a pipette inV accordance withthe present invention;

FIG. 2 is an enlarged vertical sectional view of the pipette shown inFIG. l, showing the operating mechanism of the pipette in position afterthe forward intake stroke and with dotted lines showing the push buttonportion of the plunger member in its initial position;

FIG. 3 is an enlarged fragmentary vertical sectional view showing ingreater detail a portion of the operating mechanism in the same positionas shown in FIG. 2;

FIG. 4 is a view similar to FIG. 3 showing the operating mechanism inposition after the forward dispensing stroke;

FIG. 5 is a horizontal sectional view taken along the line 5-5 of FIG. 3in the direction of the arrows;

FIG. 6 is a horizontal sectional view taken along the line 6 6 of FIG. 4in the direction of the arrows;

FIG. 7 is an enlarged exploded fragmentary unrolled two-dimensional viewof the adjoining exterior cylindrical surfaces of the indexing memberand the piston member showing the radial ridges on their respectiveadjoining end surfaces in aligned position during the course of theforward dispensing stroke, with the position of one of the keys shown indotted lines;

FIG. 8 is a horizontal sectional view taken along the line 8-8 of FIG. 3in the direction of the arrows;

FIG. 9 is a horizontal sectional view taken along the line 9 9 of FIG. 3in the direction of the arrows;

FIG. 10 is an enlarged fragmentary view showing the relative position ofthe cooperating portions of the indexing member, the piston member andthe key at the start of the forward intake stroke;

FIG. 1l is a View similar to FIG. 10 at the completion of the forwardintake stroke;

FIG. 12 is a view similar to FIG. 10 at the completion of the returnintake stroke and the start of the forward dispensing stroke; and

FIG. 13 is a view similar to FIG. l0 at the completion of the forwarddispensing stroke.

Referring to the drawings, a pipette in accordance with the presentinvention comprises a barrel 11 which is the main body or housingportion and which may be variously formed as to its specificconfiguration and is shown here cylindrical in form with a forwardtapered neck portion 12 and a projecting nozzle portion 13 having anouter end wall 14. Extending axially within the neck portion 12 and thenozzle portion 13 is a passageway 15 having a reduced diameter portion16 leading out through the end wall 14.

Rearwardly of the passageway in the form of an increased diametercounterbore is a cylindrical chamber 17 having a shoulder 18 formed atits forward end. At the rearward end of the cylindrical chamber 17 isthe form of an increased diameter counterbore is the main bore portion19 of the barrel 11, which forms with the cylindrical chamber 17 ashoulder 20. Disposed within the cylindrical chamber 17 is a removablecylindrical tube 21 which may be formed of glass, plastic or metal andwhich is in sealing engagement with the shoulder r18 by means of anO-ring 22. The cylindrical tube 21 is held in place in the cylindricalchamber 17 by means of a retaining ring 23 which is threadedly engagedwithin the main bore 19 against the shoulder 20 and the rearward end ofthe tube 21.

Disposed within the barrel 11 is a piston member indicated generally bythe reference numeral 24 and shown in the form of a stepped shaftcomprising a rearward shaft portion 25 having a rearward transverse endsurface 26, an intermediate shaft portion 27 of reduced diameter andforming with the rearward shaft portion 25 a shoulder 28, and a forwardshaft portion 29 of still further reduced diameter and forming with theintermediate shaft portion 27 a shoulder 30. The forward shaft portion29 is preferably threadedly engaged in the intermediate shaft portion 27so that the forward shaft portion 29 may be conveniently removable andreplaceable, for reasons explained more fully hereinafter. The forwardshaft portion 29 of the piston member 24 extends into the cylindricaltube 21 and is adapted to slide forwardly and rearwardly therein ineffective sealing engagement with the walls thereof as, for example, bymeans of one or more O-rings 31 around the circumference of the forwardshaft portion 29.

The intermediate shaft portion 27 and the rearward shaft portion 25 ofthe piston member 24 are disposed in the main bore portion 19 of thebarrel 11. The diarneter of the rearward shaft portion 25 is such as toenable it to slide axially along the walls of the barrel 11. Therearward shaft portion 25 is provided with one or more axially extendingslots or keyways 32 which cooperate with one or more axially extendingkeys 33 projecting inwardly from the interior walls of the barrel 11 andin engagement with the keyways 32 so as to prevent circumferentialrotation of the piston member 24 relative to the barrel 11. The rearwardtransverse end surface 26 of the rearward shaft portion 25 of the pistonmember 24 is provided with a plurality of radial teeth 35, described ingreater detail hereinafter.

Disposed within the main bore portion 19 of the barrel 11 rearwardly ofthe piston member 24 is an indexing member 37 having a forwardtransverse end surface 38 in contact with the rearward transverse endsurface 26 of the rearward shaft portion 25 of the piston member 24. Theforward transverse end surface 38 of the indexing member 37 is providedwith a plurality of radial teeth 39, described in greater detailhereinafter. Disposed axially around the circumference of the indexingmember 37 and extending from the forward transverse end surface 38 are aplurality of relatively shorter extending slots or keyways 41 and aplurality of relatively longer extending slots or keyways 42. As can beseen in FIG. 7, the relatively shorter extending keyways 41 and therelatively longer extending keyways 42 are equally spaced in alternatingrelationship to each other around the circumference of the indexingmember 37. At the rearward end of each of the relatively shorterextending keyways 41 is a shoulder 43.

l The diameter of the indexing member 37 is such as to enable it toslide axially along the walls of the barrel 11, and its position withinthe barrel with respect to the keys 33 projecting inwardly from theinterior walls of the barrel is such as to enable its keyways 41 and 42to slide into and out of engagement with the keys 33. When the keys 33are not in engagement with either the keyways 41 or 42, the indexingmember 37 is free to rotate circumferentially in relation to both thebarrel 11 and the piston member 24. When the keys 33 are in engagementwith the relatively shorter extending keyways 41, forward axial movementof the indexing member 37 within the barrel 11 is limited by theshoulder 43. On the other hand, `when the keys 33 are in engagement withthe relatively longer extending keyways 42, the indexing member 37 isfree to move forwardly within the barrel 11 a greater distance.

Disposed within the main bore portion 19 of the barrel 11 .rearwardly ofthe indexing member 37 is a plunger member indicated generally by thereference numeral 44 and comprising a plunger head `45 in Contact withthe indexing member 37, a threaded stem 46 connected to the plunger head45 and extending rearwardly therefrom and a push button 47 threadedlyconnected to the rearward end of the stem 46 and extending outwardlybeyond the rearward end of the barrel 11. To provide positive alignmentbetween the plunger member 44 and the indexing member 37, the head 48 ofthe stem 46 projects forwardly of the plunger head 45 and is receivedwithin an opening 49 in the rearward end surface of the indexing member37. A rearward reduced diameter extension 50 of the plunger head 45carries a spring member 51 for maintaining the plunger head 45 inpressure contact with the indexing member 37. The spring member 51 isheld in compression by means of a retaining ring 52 which is threadedlyengaged within the main bore 19 of the barrel 11. A shoulder 53 isformed in the bore 19 forwardly of the push button 47 to serve as 'astop means for limiting the forward movement of the plunger member 44within the barrel 11. An adjustable collar 54 is attached to the stem 46by means of a set screw 55. The collar 54 cooperates with the retain ingring 52 to limit rearward movement of the plunger member 44 within thebarrel 11.

The entire assembly within the barrel 11 is biased rearwardly by meansof a spring member 56 which is carried on the intermediate shaft portion27 of the piston member 24 and is maintained under compression betweenthe shoulder 28 of the piston member 24 and the retaining ring 23.

Removably secured in air-tight engagement to the nozzle portion 13 ofthe barrel 11 is a disposable tip 57, preferably formed of plastic,having an inlet orifice 58 at its forward end and a liquid-receivingcompartment or reservoir 59 between the orice 58 and the end Wall 14 ofthe barrel 11, in alignment with the passageway 15 in the barrel.Although the disposable tip 57 is shown in conical form secured over thenozzle portion 13 of the barrel 11 by means of a friction iit, otherforms of disposa-ble tip and other means for attaching it to the barrelmay suitably be employed. For example, the disposable tip may be in theform of a cylindrical tube removably Sec-ured in air-tight engagement tothe forward end wall of the barrel by means of a suitable retainingsleeve or collar.

Referring to FIG. 7, the radial teeth 39 on the forward transverse endsurface 38 of the indexing member 37 are formed by alternating beveledsectors 61 and 62 on the end surface 38 which slope in oppositedirections and converge alternatingly outwardly from the end surface 38to form radial ridges 63 and inwardly toward the end surface 38 to formradial grooves 64. As shown in FIG. 7, the end surface 38 is providedwith six teeth 39 having their ridges 63 equally spaced at 60 degreeintervals. The beveled sectors `61 and 62 all have substantially thesame width and substantially the same degree of slope so that eachradial ridge 63 is spaced substantially midway between a pair ofadjacent radial grooves 64. In the preferred form shown in FIG. 7, thebeveled sectors 61 and 62 are each sloped at an angle of approximately30 degrees to the horizontal transverse plane and form between them attheir intersection an angle of approximately 120 degrees. As shown inFIGS. 7 and 8, the alternating axially extending keyways 41 and 42 areso positioned around the circumference of the indexing member 37 thatthere is one keyway disposed between each pair of adjacent radial ridges63, with each keyway extending widthwise across radial groove 64 from apoint on beveled sector 61 adjacent radial ridge 63 to a point onbeveled sector 62 adjacent radial groove 64.

The radial teeth 35 on the rearward transverse end surface 26 of therearward shaft portion 25 of the piston member 24 are formed byalternating beveled sectors 65 and 66 on the end surface 26 which slopein opposite directions and converge alternatingly outwardly from the endsurface 26 to for-m radial ridges `67 and inwardly toward the endsurface 26 to form radial grooves 68. As shown in FIG. 7, the endsurfaces 26 is provided with six teeth 35 having their ridges 67 equallyspaced at 60 degree intervals. The beveled sectors 65 have a narrowerwidth and steeper slope than the beveled sectors 66, so that each radialridge 67 is more closely spaced to one of its adjacent radial grooves 68than to the other. In the preferred form shown in FIG. 7, the beveledsectors 65 and 66 are sloped at angles to the horizontal transverseplane of approximately 60 degrees and 30 degrees, respectively, and formbetween them at their intersection an angle of approximately 90 degrees.As shown in FIG. 7, the rearward shaft portion 25 of the piston member24 is provided with three axially extending keyways 32 disposed aroundits circumference at alternate radial ridges 67, with each keyway 32extending widthwise across radial ridge 67 from its more closely spacedadjacent radial groove 68 to a point on beveled sector `66 such that theradial ridge 67 lies approximately midway across the width of the keyway32.

As can be seen in FIG. 7, each key 33 is provided with a K beveledrearward end surface `69 thaving a rearwardmost edge 70 at one sidethereof. The end surface 69 slopes in the same direction and at the sameangle as beveled sector 61 on the end surface 38 of the indexing membery37, thereby facilitating sliding of these surfaces relative to eachother.

The operation of the pipette of this invention may best be understood byreference to FIGS. 2 and 10 through 13. At the start of the forwardintake stroke, with the push button 47 in the undepressed positionindicated bv the dotted lines in FIG. 2, the indexing member 37, thepiston member 24, and the keys 33 projecting inwardly from the interiorwalls of the barrel 11, are in the relative position shown in FIG. l0.In this position, the beveled sectors 62 on the forward transverse endsurface 38 of the indexing member 37 are in abutment against the radialridges `67 on the rearward transverse end surface 26 o-f the pistonmember 24, the keyways 41 and 42 on the indexing member 37 are both outof alignment with the keys 33 which are in engagement with the keyways32 on the piston member 24, and the rearwardmost edges 70 of therearward end surfaces 69 of the keys 33 are leading into the relativelyshorter extending keyways 41 and are just short of contact with theportion of the beveled sectors 61 immediately adjacent to the radialridges 63 on the end surfaces 38 of the indexing member 37.

When the push 4button 47 is depressed toward the shoulder 53, theplunger head 45 is urged forwardly against the indexing member 37, whichin turn is urged forwardly in the barrel against the piston member 24and the keys 33. The edges 70 of the keys 33 come into contact with thebeveled sectors 61 immediately adjacent to the radial ridges 63, and thebeveled sectors 61 slide forwardly along the beveled end surfaces 69 ofthe keys 33, causing counter-clockwise rotation of the indexing member37 relative to the keys 33 and the piston member 24. The rotationalforce thus imparted to the indexing member 37is sufficient to overcomethe resistance of the radial ridges 67 of the piston member 24 againstthe beveled sectors 62 of the indexing member 37, enabling the beveledsectors 62 to slide over the ridges 67 until the ridges 67 are clearedby the radial ridges 63 of the indexing member 37. Upon further forwardmovement of the indexing member 37 in the barrel, the beveled sectors 61of the indexing member, which slope in the same direction and at thesame angle as the lbeveled sectors 66 of the piston member, slide alongthe beveled sectors 66, thereby causing further counter-clockwiserotation of the indexing member until the keyways 41 on the indexingmember are brought into alignment with the keys 33. Further forwardmovement of the indexing imember in the barrel, with keys 33 inengagement with the keyways 41, urges the piston member 24 forwardly inthe barrel, thereby causing the forward shaft portion 29 of the pistonmember to slide forwardly in the cylindrical tube 21 in sealingengagement with the walls thereof so as to expel air through thepassageway 15 and 16 and the reservoir 59 and orice 58 of the tip 57. Asthe piston member 24 moves forwardly in the barrel, the spring member 56is .further compressed between the shoulder 28 of the piston member andthe retaining ring 23. Forward movement of the assembly in the barrel isbrought to a positive stop when the keys 33 come into abutment againstthe shoulders 43 at the rearward ends of the keyways 41, as shown inFIG. l1. As can be seen in FIG. 2, the positive stop at the completionat the forward intake stroke leaves the push button 47 still spaced fromthe shoulder 53 and extending outwardly beyond the rearward end of thebarrel.

At this point the tip 57 is submerged in the liquid to be transferred,and the intake stroke is completed by releasing the push button 47,whereupon the compressed spring member 56 urges rearwardly on theshoulder 28' of the piston member 24, causing the forward shaft portion29 of the piston member to slide rearwardly in the cylindrical tube 21in sealing engagement with the walls thereof so as to draw apredetermined volume of the liquid through the orifice 58 into thereservoir 59 of the tip 57.

As the piston member 24 is urged rearwardly in the barrel by theresiliency of the compressed spring member 56, the beveled sectors `66on its rearward transverse end surface 26 bear directly against thebeveled sectors 61 on the forward transverse end surface 38 of theindexing member 37, creating a force directed perpendicularly to thebeveled sectors 161, or, in other words, in the direction of the slopeof beveled sectors '65. While the keyways 41 on the indexing member 37are in engagement with the keys 33, this force is restricted to actingonly in an axial direction, urging the indexing member rearwardly in thebarrel. However, when the keyways 41 become disengaged from the keys 33,the force is able to act also in a transverse direction, causingcounter-clockwise rotation of the indexing member relative to the pistonmember and the keys and thus bringing the keyways 41 out of alignmentwith the keys. The counter-clockwise rotation is limited by the beveledsectors 62 of the indexing member coming into abutment against theradial ridges 67 of the piston member, thereby bringing the members intothe position shown in FIG. 12.

The indexing member 37, as it is urged rearwardly in the barrel, in turnurges rearwardly against the plunger head 45, causing the push button 47to return to its initial position indicated by the dotted lines in FIG.2. Rearward movement of the assembly in the barrel is limited by thecollar 54 coming into abutment against the retaining ring 52.

At the completion of the return intake stroke and the start of theforward dispensing stroke, the indexing member 37, the piston member 24,and the keys 33 are in the relative position shown in FIG. l2, whichdilfers from their relative position at the start of the forward intakestroke shown in FIG. l and described above, only in that therearwardmost edges 70 of the rearward end surfaces 69 of the keys 33 arenow leading into the relatively longer extending keyways 42 of theindexing member. The movement of the parts within the barrel during thedispensing stroke is the same as that described above for the intakestroke, with the exception that the counterclockwise rotation of theindexing member 37 on the forward portion of the dispensing strokebrings the relatively longer extending keyways 42 into alignment withthe keys 33. The indexing member is then free to slide forwardly alongthe keys 33- in the `barrel a greater distance than was possible on theintake stroke, as shown in FIG. 13, with forward movement of theassembly in the barrel being brought to a positive stop when the pushbutton 47 cornes into abutment against the shoulder 53. The forwardshaft portion 29 of the piston member 24 is hence caused to slideforwardly in the cylindrical tube 21 a distance greater than thattraveled during the intake stroke. Such overtravel serves to force outof the reservoir 59 of the tip 57 any trace amounts of the liquid whichmight otherwise remain therein, thereby insuring that all of thepredetermined volume of liquid drawn into the reservoir 59 on the intakestroke is completely dispensed on the dispensing stroke.

At the completion of the return dispensing stroke, the indexing member37, the piston member 24, and the keys 33 have been returned to therelative position shown in FIG. 10, and the pipette is thus ready forthe next filling and dispensing cycle.

Although for purposes of illustration, the cooperating means foreffecting circumferential rotation of the indexing member 37 relative tothe keys 33 has been described with some particularity in regard to thenumber, relative position, configuration and dimensions of the radialteeth 39 and keyways 41 and 42 on the indexing member 37 and the radialteeth 35 and keyways 32 on the piston member 24, it will be understoodthat some variation rnay be made therein without significantly changingthe basic operating mechanism described above. For example, thealternating axially extending keyways 41 and 42 may be so positionedaround the circurneference of the indexing member 37 that there is onekeyway at each radial ridge 63, extending vwidthwise from a point onbeveled sector `61 adjacent radial ridge 63, across radial ridge 63, tothe adjacent radial groove 64. Moreover, the rearward transverse endsurface 26 of the piston member 24 may be provided with three radialteeth 35 instead of six, having their ridges 67 equally spaced at 120degree intervals, either at or between the keyways 32.

The predetermined volume of the liquid to be drawn into the reservoiris, of course, dependent on the volume of air expelled therefrom on theforward intake stroke, and may be varied by varying the inside diameterof the cylindrical tube 21 and, correspondingly, the diameter of theforward shaft portion 29 of the piston member 24. For this reason, it ispreferred to have both of these parts conveniently removable andchangeable, as described above. Thus, if it is desired to increase thepredetermined volume of the liquid to be drawn into the reservoir, thelcylindrical tube 21 may be removed from t'ne cylindrical chamber 17 byunthreading the retaining ring 23 and replaced with a similarcylindrical tube having a larger inside diameter, and the forward shaftportion 29 may be Unthreaded from the intermediate shaft portion 27 andreplaced with a similar forward shaft portion having a larger diameterslidable in sealing engagement with the walls of the larger insidediameter cylindrical tube.

Finer adjustment of the predetermined volume of the liquid to be drawninto the reservoir may be effected by means of the adjustable collar 54attached to the stem 46. For example, by setting the collar 54 moreforwardly on the stem 46, the entire displaceable assembly within thebarrel will assume a more rearward initial position relative to thebarrel, thereby increasing the length of the stroke and thus the volumeof air expelled thereby.

The disposable tip 57 attached to the forward end of the barrel issuitably selected so as to have an appropriate reservoir capacity foraccommodating the predetermined volume of liquid to be transferred. Thepipette of the present invention is most suitably adapted for use intransferring volumes of liquid within the range of from about 5 to about2000 microliters, In general, three different capacity tips will besufficient for use over this range, i.e., a small capacity tip forvolumes within the range of from about 5 to about 100 microliters, amedium capacity tip for volumes within the range of from about to about100G microliters, and a large capacity tip for volumes within the rangeof from about 1000 to about 2000 microliters,

The various parts constituting the pipette of this invention maysuitably be fabricated from various materials including both metal andplastic. Particularly good results have been obtained when employingaluminum for the barrel 11 and the push button 47, nylon for theindexing member 37 and the rearward and intermediate shaft portions 25and 27 of the piston member 24, stainless steel for the forward shaftportion 29 of the piston member 24, the stem 46 and the plunger head 45,and glass for the cylindrical tube 21.

The barrel 11 is generally made in at least two threadedly engagedsections so that convenient access may be had to the interior thereoffor removing and replacing the cylindrical tube 21 and the forward shaftportion 29 of the piston member 24. For ease in manufacturing when thebarrel is fabricated from metal, it is made in three threadedly engagedsections, as shown in FIG. 2. The rearward section 81 has a forwardexternally threaded portion 82 of reduced outside diameter. The keys 33are formed internally along the portion 82. Threadedly engaged aroundthe outside of the portion 82 is an internally threaded intermediatesleeve section 83 and a forward section 84 internally threaded at itsrearward end and housing the cylindrical tube 21. Separation of theforward section 84 from the other two sections 81 and 83 provides readyaccess to the cylindrical tube 21 and the forward shaft portion 29 ofthe piston member 24.

It will, of course, be understood that various changes and modificationsmay be made in the form, details, arrangement and proportions of thevarious parts of the pipette shown and described herein withoutdeparting from the spirit and scc-pe of the present invention, which isnot to be limited to the specific embodiments shown and describedherein.

We claim:

1. A pipette comprising in combination, a barrel having a forward endand a rearward end, a pistou member slidable forwardly and rearwardly insaid barrel, an indexing member in operative contact with said pistonmember rearwardly thereof, said indexing member being slidable axiallyin said barrel and being circumferentially rotatable relative to saidbarrel, a plunger member in operative contact with said indexing memberrearwardly thereof and movable axially within said barrel, meansyieldably urging said piston member rearwardly in said barrel, a firstset of cooperating means on said indexing member and said barrel forpreventing forward axial movement of said indexing member in said barrelbeyond a preselected distance, a second set of cooperating means on saidindexing member and said barrel for permitting axial movement of saidindexing member beyond said preselected distance, that portion of eachof said first and second sets of cooperating means on said indexingmember being circumferentially spaced apart thereon, androtation-causing means responsive to a forward and return stroke of saidplunger member in said barrel causing restricted circumferentialrotation of said indexing member relative to said barrel, wherebysuccessive forward strokes of said plunger member in said barrel effectsalternating engagement of said first and second sets of cooperatingmeans.

2. The pipette of claim 1 wherein said rotation-causing means comprisesa forward stroke-responsive means and a return stroke-responsive means,said forward strokeresponsive means causing restricted circumferentialrotation of said indexing member relative to said barrel so as to bringinto alignment one of said rst and second sets of cooperating means, andsaid return stroke-responsivemeans causing further restrictedcircumferential rotation of said indexing member relative to said barrelso as to bring said aligned set of cooperating means out of alignment.

3. The pipette of claim 2 wherein said forward strokeresponsive meanscomprises beveled radial teeth extending forwardly from the forwardtransverse end surface of said indexing member and, cooperativetherewith, at least one inwardly extending projection on the interiorwalls of said barrel.

4. The pipette of claim 3 wherein said forward strokeresponsive meansfurther comprises beveled radial teeth extending rearwardly from therearward transverse end surface of said piston member cooperative withsaid teeth on said indexing member.

5. The pipette of claim 2 wherein said return strokeresponsive meanscomprises beveled radial teeth extending forwardly from the forwardtransverse end surface of said indexing member and, cooperativetherewith, beveled radial teeth extending rearwardly from the rearwardtransverse end surface of said piston member.

6. The pipette of claim 1 wherein that portion of said first and secondsets of cooperating means on said barrel comprises at least one inwardlyextending projection on the interior walls of said barrel, that portionof said rst set of cooperating means on said indexing member comprises aplurality of relatively shorter axially extending keyways, and thatportion of said second set of cooperating means on said indexing membercomprises a plurality of relatively longer axially extending keyways,said relatively shorter extending keyways and said relatively longerextending keyways being equally spaced in alternating relationship toeach other around the circumference of said indexing member.

7. The pipette of claim 1, including cooperating means on said barreland said piston member preventing circumferential rotation of saidpiston member relative to said barrel.

8. The pipette of claim 7 wherein said cooperating means preventingcircumferential rotation of said piston member relative to said barrelcomprises at least one axially extending keyway on the exterior surfaceof said piston member and at least one inwardly extending projection onthe interior walls of said barrel, said keyway and said projection beingaxially slidable relative to each other.

9. The pipette of claim 1, including a hollow tip portion removablysecured in air-tight engagement to said forward end of said barrel, saidtip portion having a liquid-receiving compartment having its forward endopen to the atmosphere and its rearward end in communication with theinterior of said barrel, whereby upon rearward movement of said pistonmember relative to said barrel, liquid is adapted to be drawn into saidtip short of said barrel, and upon subsequent forward movement of saidpiston member relative to said barrel, said liquid is adapted to bedispensed from said tip.

10. The pipette of claim 1 wherein said barrel has removably securedtherein adjacent its forward end of cylindrical tube having an internaldiameter less than that of said barrel, and said piston member has arearward portion slidable forwardly and rearwardly in said barrel and aforward portion of reduced diameter slidable forwardly and rearwardly insaid tube, said forward portion of said piston member being removablysecured to said rearward portion of said piston member.

References Cited UNITED STATES PATENTS 6/1964 Weisser 401-111 8/1967Hamilton 222-386 X U.S. Cl. XR. 222-386; 401-111

